The Duke and Duchess of Cambridge have sent their "thoughts and prayers" to the victims of the gay nightclub massacre in Orlando.
Lone gunman Omar Mateen, 29, left 49 people dead and dozens of others wounded in the massacre at Pulse in the Florida city on Sunday.
William and Kate visited the American Embassy in central London on Tuesday to sign a book of condolence.
Dressed in black, the royal couple were greeted by the US Ambassador Matthew Barzun before writing individual messages.
The Duke paused for a moment to read the ambassador's dedication as his wife stood solemnly by his side.
He wrote: "With our deepest condolences and with our thoughts and prayers to all those affected."
The Duchess signed "Catherine" beside her husband's name.
The couple then spoke to embassy staff who have worked on LGBT issues.
Dozens of embassy workers, all wearing custom-made badges with a combination of the American, British and Pride flags, filled the lobby for the royal visit.
An image of their messages will be added to an online condolence book which the public are able to contribute to.